<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        h1{
            color: red;
        }
        .title{
            color: aqua;
        }
        #title{
            color: aquamarine;
        }
        h1:hover{
            color: rgb(0, 0, 0);
        }
        #title::before{
            content: "前面添加的内容";
            color: brown;
        }
        #title::after{
            content: "后面添加的内容";
            color: chartreuse;
        }
    </style>
</head>
<body>
    <h1>标题</h1>
    <h1 class="title">标题</h1>
    <h1 id="title">标题</h1>
    <h1>标题 <span style="color: blue;font-size: 16px;">副标题</span></h1>
</body>
</html>